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Linux kernel 6.6.157.1-1 can deadlock when moving files
published 2 months ago
Summary
The Linux kernel version 6.6.157.1-1 may cause the system to freeze if a request tries to move data blocks between files that are on different file systems. This can happen during normal file‑copy or move operations that involve overlay or similar layers, leading to a deadlock where the system stops responding. Updating to a kernel that includes the fix will prevent the freeze.
What to do
The CVE record does not list a fixed version. Check the vendor's site or the advisory links below - a fix may already be released.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| Azure Linux:3 | azure | kernel | <= 6.6.150.1-1 |
| Azure Linux:3 | – | kernel |
<= 6.6.152.1-1 <= 6.6.157.1-1 |
Original advisory text
CVE-2026-74307 affecting package kernel 6.6.157.1-1
In the Linux kernel, the following vulnerability has been resolved:
ext4: validate donor file superblock early in EXT4_IOC_MOVE_EXT
Reject the EXT4_IOC_MOVE_EXT ioctl early if the donor file does not
belong to the same superblock as the original file. Currently, this
validation is performed inside ext4_move_extents() by
mext_check_validity(), but only after lock_two_nondirectories() has
already acquired the inode locks. When the donor fd refers to a file
on a different filesystem (e.g., overlayfs), this late validation
creates a circular lock dependency:
CPU0 (overlayfs write) CPU1 (ext4 ioctl)
---- ----
inode_lock(ovl_inode)
mnt_want_write_file(filp)
sb_start_write(ext4_sb) [sb_writers]
backing_file_write_iter()
vfs_iter_write(real_file)
file_start_write(real_file)
sb_start_write(ext4_sb) [blocked by freeze]
lock_two_nondirectories()
inode_lock(ovl_inode) [blocked]
With a concurrent freeze operation holding sb_writers write side, this
forms a deadlock cycle: CPU0 waits for freeze to complete, freeze waits
for CPU1's sb_writers reader to exit, CPU1 waits for CPU0's inode lock.
Since EXT4_IOC_MOVE_EXT exchanges physical extents between two files,
it fundamentally requires both files to reside on the same ext4
filesystem. Moving the superblock check before any lock acquisition
is both semantically correct and eliminates the circular dependency
by ensuring that cross-filesystem donor fds are rejected before
sb_writers or inode locks are taken.
ext4: validate donor file superblock early in EXT4_IOC_MOVE_EXT
Reject the EXT4_IOC_MOVE_EXT ioctl early if the donor file does not
belong to the same superblock as the original file. Currently, this
validation is performed inside ext4_move_extents() by
mext_check_validity(), but only after lock_two_nondirectories() has
already acquired the inode locks. When the donor fd refers to a file
on a different filesystem (e.g., overlayfs), this late validation
creates a circular lock dependency:
CPU0 (overlayfs write) CPU1 (ext4 ioctl)
---- ----
inode_lock(ovl_inode)
mnt_want_write_file(filp)
sb_start_write(ext4_sb) [sb_writers]
backing_file_write_iter()
vfs_iter_write(real_file)
file_start_write(real_file)
sb_start_write(ext4_sb) [blocked by freeze]
lock_two_nondirectories()
inode_lock(ovl_inode) [blocked]
With a concurrent freeze operation holding sb_writers write side, this
forms a deadlock cycle: CPU0 waits for freeze to complete, freeze waits
for CPU1's sb_writers reader to exit, CPU1 waits for CPU0's inode lock.
Since EXT4_IOC_MOVE_EXT exchanges physical extents between two files,
it fundamentally requires both files to reside on the same ext4
filesystem. Moving the superblock check before any lock acquisition
is both semantically correct and eliminates the circular dependency
by ensuring that cross-filesystem donor fds are rejected before
sb_writers or inode locks are taken.
References
Timeline
Published15 Aug 2026
Updated24 Sep 2026
First seen23 Sep 2026
Sources
AZL-96462 · OSV
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